This invention relates to matrix structures and more particularly to matrix structures comprised of ceramic material. Even more particularly, the invention relates to annular ceramic matrix structures adapted for use in heat regenerators typically found in many turbine engines.
Ceramic structured heat regenerators have found wide acceptance in many of today's turbine engine industries. Engines of this variety are desired in the automotive and aircraft fields primarily because of their high operating efficiencies. Such high efficiencies are in turn the result of the regenerator's ability to recover waste heat losses and to preheat air coming into the engine. Accordingly, a decrease in the level of fuel consumption and noxious exhaust emissions can be expected.
In most cases, the heat regenerator is an annular member which slowly rotates within the turbine engine during operation. The ceramic structure of the regnerator is comprised of a plurality of alternating corrugated and flat ceramic strips which define a plurality of cellular flow passages axially oriented about the axis of rotation of the member. Exhaust gases which are emitted from the engine's combustion region pass through a portion of this regenerator and thus serve to heat said portion. As the heated portion is rotated to the region of the engine through which passes the incoming cool air, this air is heated. As is well understood in engine technology, preheated air having a quantity of fuel therein is more easily ignited than cool air having same. The result is an immediate increase in engine efficiency.
A particular problem with known ceramic matrix structured heat regenerators of the rotary variety is their relatively low strength. As can be appreciated, several stresses e.g. compressive and tensile, are present during operation of the turbine's regenerator and in many cases, several regenerators have failed due to these stresses.
Stresses are also present in the formation of the ceramic structure from the green (unfired) to the completed (fired) state. During the firing operation, stresses are induced as a result of the shrinkage of the green ceramic, said shrinkage resulting from the removal of plastic forming aids present in most ceramic compositions. Usually, a structure of ceramic particles dispersed in about 30 percent by weight of a plastic supporting matrix exhibits a shrinkage during firing within the range of from about 3 to 12 percent, with a 5-6 percent range typically occurring.
It is believed therefore that an improved ceramic matrix structure and method for making same wherein the resulting structure exhibits a significantly increased strength against stresses typically occuring during most known matrix forming processes as well as those present in most turbine engine operations would constitute an advancement in the art.